C :: Qsort With Array Initialized Using Malloc?
Mar 2, 2013
I want to be honest, this is FOR homework, but is NOT homework. I have created this example to work from in order to understand qsort further because the next assignment requires it's use.
Our teacher gave us this small piece of example code and I am trying to expand on it to serve my purpose.
[C] Sorting - Pastebin.com
The code gives me no errors, but does not sort the array. Need to clarify the use of qsort in this instance.
I am imagining that the reason it's not sorting properly ( or at all ) is because of my comparison function. That is really just an assumption. Or perhaps I just don't understand the pointer array i'm using.
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Mar 31, 2013
I am versed in qsorting struct members within a struct instance, as in the example below:
Code:
#include <iostream>
#include <stdlib.h>
using namespace std;
struct item_database {
[Code]....
What I CANT do however is to sort an array of structs by one of its members. This is a complete different problem even if it sounds similar.
In other words, the problem is this; Say we have a struct:
Code:
struct item_database {
int key;
string token;
};
Then we declare an array of this struct in the heap:
Code: item_database *idptr = new item_database[700000]; and initialize its values.
How would one go about sorting this heap array of structs by its member function "token"?
I used the following call to qsort (standard library) and call to the compare function but it doesnt work:
Code:
qsort (idptr, 1000, sizeof(string), compare);
Code: int compare (const void* a, const void* b){
if (*(char*)a >= *(char*)b)
return 1;
else
return -1;
}
Or in more lamens terms say we have the following stuct instances:
Key: Token:
1 Hello
2 World
3 How
4 Are
5 You
Then I need those structs to order according to token (alphabetically, increasing or decreasing depending whats in our compare function).....
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Sep 26, 2014
I am starting a new thread. So I try to sort an array with qsort and then save the new order, so this means if I have a list like:
4 3 7 2 [0] [1] [2] [3],
after sorting it becomes:
2 3 4 7 [3] [1] [0] [2] <== this is what I want to have!
Which works fine, with following code:
void qsort_my(int *a, int l, int r, int *array_order) {
int j;
if( l < r ) {
j = split( a, l, r, array_order);
qsort_my( a, l, j-1, array_order);
qsort_my( a, j+1, r, array_order);
[Code]...
I tried to add the criteria :
(if (a[i] != a[j] || (a[i] == a[j] && array_order[i] > array_order[j])))
before calling switch_pos, but it is not working since sometimes you swap two numbers like:
11 9 15 9 <= here the 11 and 15 are swapped, but the two 9's will never be swapped <=> compared.I mean I could run it again with the array_order on the first parameter position, but this would increase my runtime enormously!
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Sep 1, 2014
I have a `char*` data-member in a class.
I get the following compiler error, the error refers to the char* data member:
error C4351: new behavior: elements of array will be default initialized.
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Sep 1, 2014
I have a `char*` data-member in a class.
I get the following compiler error, the error refers to the char* data member:
error C4351: new behavior: elements of array will be default initialized.
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Apr 3, 2013
How do I copy from a dynamic array initialized in a class but with a different memory address. For example if my array is a dynamic array initialized in a class...
Code:
const int CAPACITY=5;
class Array{
public:
Array();//constructor
[Code] .....
How would i copy this array to a another array but have a different memory address so when i deallocate array a my copy array also isn't deallocated.
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Apr 7, 2014
The following:
Code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main(int argc, char *argv[]) {
int i;
int arr[3];
[Code] ....
Notice we didn't set a value for second index but it returns 0. Should I assume that when declaring an array with n values, those values will be initialized to 0 automatically or should I still initialize the array with all 0s doing something like this:
Code:
for(i=0;i<sizeof(arr);i++) {
arr[i]=0;
}
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Oct 30, 2013
This is what I have so far
My function does not work and my compiler says my int array is not initialized
#include <iostream>
#include <cctype>
#include <string>
#include <fstream>
#include <stdio.h>
using namespace std;
void arrayToFile(ofstream tak, int *arr[], int size )
[Code] ...
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Nov 6, 2013
Im supposed to create an array of eight Circle objects initialized with the radii which is in the program. Also I must use bubble sort to arrange the objects is ascending order.
ERRORS:
'initializing' : cannot convert from 'double' to 'Circle'
'setRadius' : is not a member of 'Circle'
see declaration of 'Circle'
'findArea' : is not a member of 'Circle'
see declaration of 'Circle
#include "stdafx.h"
#include <iostream>
#include <iomanip>
using namespace std;
class Circle {
[Code] ....
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Dec 15, 2013
i want to ask how does malloc works on an array for instance can i dao this
Code: p=100;
int array[10];
array = malloc(p * sizeof(int));
then will the size of int be 100 so will i be able to do like
Code:
array[11] = 12 ; ???
also if i have a 2d array how can i use malloc on it and how does this works with pointers????
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Mar 30, 2013
I am able to work with n instances of a structure in one mallocated area, but when I try to do the same thing with just character pointers, I get compiler errors about making integer from pointer without a cast. If I create a structure with just a character pointer in it, it works just fine... I am just not seeing something here!!!
This works:
Code:
#include <stdio.h>
#include <stdlib.h>
int main (void) {
struct items {
unsigned int item_1;
unsigned int item_2;
[Code]...
This DOES NOT work!
Code:
#include <stdio.h>
#include <stdlib.h>
int main (void) {
char * items_ptr = NULL;
unsignedint i = 0;
char * one = "one";
char * two = "two";
[Code]...
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Mar 2, 2015
I made a program that adds two matrices and displays their sum with a max dimension of 100.
/* This program asks the user for 2 matrices called A and B, as integers,
and displays their sum, C. The max dimension of each matrix is 100. */
#include <stdio.h>
// Construct function
void construct() {
int m, n, i, j; // Variables
int first[100][100], second[100][100], sum[100][100]; // Matrices variables
[Code] ....
Now I need to change it so there is no max size for each matrix. The arrays will be larger than 100x100 so I need to use malloc to create my arrays. So I cant use int A[rows][cols]. This is what I did to covert arrays to malloc. It compiles but it crashes after I entered all the integers.
/* This program asks the user for 2 matrices called A and B, as integers,
and displays their sum, C. The max dimension of each matrix is 100. */
#include <stdio.h>
#include <stdlib.h>
// Construct function
void construct() {
int m, n, i, j; // Variables
int *first = NULL;
[Code] .....
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Oct 16, 2013
I am attempting to change a character in a character array.In the code below, there are three attempts to do this. Only the first one will succeed. The last two both segfaults. If I understand correctly, str_one is declared in the heap, and could therefore be manipulated; and in contrast, str_two is declared in the stack and is therefore immutable, thus the segfault, when update it is attempted. However, I understand that using malloc, one is able to assign a pointer and allocate space in heap memory. Thus, I should be able to manipulate the assigned variable str_three. Doing so, however, results in a segfault.
Code:
#include <stdio.h>
#include <stdlib.h>
int main (int argc, char const* argv[])
{
char str_one[4092] = "This is string number one";
char * str_two = "This is string number two";
[Code]...
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Mar 10, 2014
What is wrong with my function why does it spit out huge numbers? And how do i use malloc or calloc to create an array in dynamic memory, and return a pointer to this array
Code:
#include <stdio.h>#include <stdlib.h>
int fibonacci(int n)
{
int i;
long int fib[40];
fib[0]=0;
fib[1]=1;
for(i=2;i<n;i++){
fib[i] = fib[i-1] + fib[i-2];
[Code]....
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Mar 20, 2013
i am facing some problem with qsort() function it work well if the last element of array is larger then the 2nd last element. But in case if last element of array is smaller then the 2nd last it will sort the whole array and remains the last as it is. For example
Code:
int group_id_local[max_j]={2,1,4,5};// it work fine, output should be {1,2,4,5} but if i have this one
int group_id_local[max_j]={2,1,4,3};
// output should be {1,2,4,3}
/* COMPARE FUNCTION FOR USING QSORT()*/
int cmpfunc (const void* a, const void* b)
{
if (*(int *)a < *(int *)b) return -1;
if (*(int *)a > *(int *)b) return 1;
return 0;
[Code]....
why it will not sort the last element?
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Sep 28, 2014
How do i sort numbers from highest to lowest using qsort? I dont have a code. I dont know how to use this one.
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Nov 8, 2014
I almost finished a program but am stuck on sorting the hand im dealing with qsort. sorting by the face values and if they have the same faces im suppose to follow this suit order to determine which one is greater (Clubs, Diamond, Hearts, and Spades) how would i adjust my comparator function to do this for me ?
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define DECK_SIZE 52
struct card {
const char *face;
const char *suit;
[code]....
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May 6, 2013
I have declared and initialized where needed but keep getting a Debug Error: Variable F is being used without being initialized.
Code:
#include "stdafx.h"
#include<stdio.h>
void Signboard (void)
{
/* This function prints the Signboard onto the output page */
int n;
}
[code]....
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Jan 27, 2013
#include<iostream>
#include<iomanip>
#include<fstream>
#include<string>
#include<cmath>
using namespace std;
int studentdetails_mean();
double standard_deviation();
[Code] .....
its showing Run-Time Check Failure #3 - The variable 'mean' is being used without being initialized.
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Jan 16, 2014
There is error that said run time check failure 3 the variable p is being used without being initialized
typedef struct portion{
char type[8]; float pctg;
struct portion *next;
}Portion;
typedef struct student{
char ID[9]; float cmark;
Portion *head;
[Code] .....
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May 20, 2014
Why pointer cannot be initialized with a constant like.
Code: int *p = 3000;
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Mar 14, 2013
It said my width1 is being used wihtout being initialized.. what does it mean?
#include<iostream>
using namespace std;
double Area(double height, double width);
double Perimeter(double height, double width, double height1, double width1);
[Code] .....
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Oct 13, 2014
I just finished coding a program that is based on polymorphism and inheritance but when I ran the program it crashed? I do not know what is the cause of the program crashing.
#include<iostream>
#include<string>
using namespace std;
class Shape{
float density;
[code].....
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Jan 27, 2015
I get an error when i try to compile this code. I tried to allocate memory in main function and that works. But why it doesn't work in function? I think that there is something wrong with function argument, but not sure.
Code:
#include <iostream>
#include <fstream>
using namespace std;
struct Word
[Code].....
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Jan 12, 2012
I hope I got all the jargon correct. I have something like this:
Code:
const Fl_Color my_fl_dark_gray=fl_color_cube(64*(FL_NUM_RED-1)/255, 64*(FL_NUM_GREEN-1)/255, 64*(FL_NUM_BLUE-1)/255);
in a header file and the header file is included in several C files.
Questions:
At run time,
Is there just one copy of the const variable my_fl_dark_gray or are there multiple copies for the multiple C files?If a function uses the const variable, does the initialization statement "my_fl_dark_gray=fl_color_cube(...);" run every time the function is called or does it just run once and then when the function is called it just uses the value stored in memory?
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Mar 15, 2014
I am writing a program to calculate a rectangle's area.
Eg.
Enter top left point: 1 1 (User input)
Enter bottom right point: 2 -1 (User input)
Top Left x = 1.000000 y: 1.000000
Bottom Right x = 2.000000 y: -1.000000
Area = 2.000000 (Program output)
It keeps on prompting me my variable r is being used without being initialized, when I think I already did so.
Code:
typedef struct {
double x;
double y;
} Point;
[Code] ....
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